The long-term goal of this application is to define the molecular mechanisms that govern the morphological differentiation and functional maturation of a unique class of inhibitory GABAergic interneurons, called chandelier cells (ChCs). These cells are typified by their distinctive axonal morphology with arrays of boutons termed cartridges, and play a central role in maintaining proper nervous system function. Significantly, ChC morphological and functional perturbations are found in common brain disorders, including epilepsy and schizophrenia. Despite the importance of these cells, the molecular mechanisms that regulate ChC morphogenesis remain largely unknown. Our studies initiated to gain insight into the role of Rho regulators in GABAergic interneurons revealed a critical role for the DOCK180 family member DOCK7/Zir2, an activator of Rac, in the morphological differentiation of ChCs. This was made possible by implementing an innovative method that enables genetic labeling and manipulation of single ChCs in situ in developing mouse embryos. Furthermore, we recently found that DOCK7 forms a complex with the schizophrenia-linked ErbB4 tyrosine kinase receptor, which notably the only other protein is so far shown to affect ChC morphogenesis. These findings provide a unique entry point for studies of the molecular basis of ChC morphogenesis and function. This application aims to further define the role of DOCK7 in ChCs, and in particular to identify the molecular pathways DOCK7 is integral to. Towards these goals, the first aim will test the hypothesis that altered DOCK7 expression impacts not only the morphology but also the physiological properties of ChCs. Specifically, we will manipulate DOCK7 levels in a large population of ChCs visualized via GFP marker protein expression in a genetically modified mouse line, which will permit electrophysiology studies of these cells. Aim 2 focuses on the regulation of DOCK7 in ChCs. We conjecture that DOCK7 acts as downstream effectors of ErbB4 to control ChC morphogenesis and function. We will test this hypothesis using molecular, biochemical and genetic approaches and will further define DOCK7 regulatory elements important for this interaction and for DOCK7 function in ChCs. Finally, aim 3 scrutinizes molecular mechanisms downstream of DOCK7 in ChCs. Our preliminary data imply that both Rac-dependent and Rac-independent pathways are involved in mediating DOCK7's effects in ChCs. Hence, we will strive to characterize the Rac-mediated signaling pathways involved and identify novel molecular interactions that mediate DOCK7 function using innovative genetic and molecular approaches. The proposed studies will provide first/vital information on the molecular mechanisms governing ChC differentiation and function. As such, they could shed novel light onto the signaling defects that underlie neurological and mental disorders, such as epilepsy and schizophrenia.